The objectives of the proposed research are as follows: 1. To identify factors in burned skin which permit a rapid multiplication of Pseudomonas aeruginosa. 2. To assess the contribution of the protein exotoxin produced by P. aeruginosa growing at the burned site to the outcome of the infection. 3. To determine the relevance of this exotoxin in a human pseudomonas infection. 4. To study the initial binding and subsequent internalization of purified toxin by mammalian cells in culture and to ascertain if this is related to sensitivity of specific cells to toxin action. All of thses objectives are related to characterizing the infection of burned tissue by P. aeruginosa. An experimental burned mouse model will be used to determine the amount of toxin produced by proliferating bacteria, its concentration in the circulation and its effect on various tissues. A survey will be made of the toxin sensitivity of cells from several different animal species; uptake of labeled toxin by representative cells will be monitored.